Small problem about a plug fuse

GDB2222

Bendy_House said:

GDB2222 said:

I loaned an extension reel to a builder, who attached a wallpaper steamer to it, but didn’t bother to pull all the cable out of the reel. By the time the fuse 'blew', the insulation on the cable inside the reel had melted completely. If it had cooked a bit more inside there before the conductors touched, it might have caught fire. 

Curiously, it was the 30A MCB that switched itself off, rather than the 13A fuse in the plug. Or, maybe they both went at the same time, as I don’t remember checking the plug fuse afterwards. 

That is weird.

I wonder if perhaps the RCD went? Or the MCB was actually an RCBO?

Or, most likely, both the fuse and MCB did go simultaneously.

When cables heat up, their resistance increases. There is also, I understand, an inductive resistance (impedance?) when a cable is coiled, and both of these would surely have had the effect of reducing the overall current flow drawn by the steamer. So, most likely, the wires did end up touching.

 

  The whole house was rewired before we moved in, and we don’t have RCDs. I did say the conductors were touching, by the way. 

The PVC cable insulation was just a gloopy soup. I’m not sure what temperature PVC melts at, but it’s apparently lower than the temperature it catches fire at.   

Edit: I’m catastrophising. The Www says that PVC melts at 100-200C, presumably depending on additives. It’s apparently quite resistant to catching fire, and it needs to get to 400C . 

So, my cable reel was at the melting stage, not the catching fire stage. It does smell awful when it gets hot, though!

Bendy_House

Ah, soz, so most likely both would have tripped simultaneously.

What do you have if not RCDs? RCBOs?

GDB2222

Bendy_House said:

Ah, soz, so most likely both would have tripped simultaneously.

What do you have if not RCDs? RCBOs?

No RCDs. RCBOs neither. This was a new installation in 1998, and I think that we may have been a couple of years early. 

We are thinking of selling the house soon, and whoever buys it will be doing a major refurbishment, anyway.  The house next door has a one year refurbishment underway at the moment. You gotta have bling, apparently. So, lack of RCDs won’t matter.

Eldi_Dos

GDB2222 said:

Bendy_House said:

GDB2222 said:

I loaned an extension reel to a builder, who attached a wallpaper steamer to it, but didn’t bother to pull all the cable out of the reel. By the time the fuse 'blew', the insulation on the cable inside the reel had melted completely. If it had cooked a bit more inside there before the conductors touched, it might have caught fire. 

Curiously, it was the 30A MCB that switched itself off, rather than the 13A fuse in the plug. Or, maybe they both went at the same time, as I don’t remember checking the plug fuse afterwards. 

That is weird.

I wonder if perhaps the RCD went? Or the MCB was actually an RCBO?

Or, most likely, both the fuse and MCB did go simultaneously.

When cables heat up, their resistance increases. There is also, I understand, an inductive resistance (impedance?) when a cable is coiled, and both of these would surely have had the effect of reducing the overall current flow drawn by the steamer. So, most likely, the wires did end up touching.

 

The PVC cable insulation was just a gloopy soup. I’m not sure what temperature PVC melts at, 

This is something manufacturer's of large cable,especially multi core telecomm, have to take into account in hot weather.

If cables are not given enough time to cool down before being put on drum and battened up then put in hot yard in the sun ,the inner couple of rings can "cook" as heat builds up and can affect the insulation.

Expensive to rectify if allowed to happen as cables are usually installed before problem becomes apparent.

The extra cooling time required slows production down quite a bit in very hot weather.